Clay soil is made up of fine, easily compacted particles. Compacted soils are easily saturated, with water pooling on top. Although water pools on the surface, the underlying soil can be water deficient. Limited aeration and water makes this soil unsuited for root crops, but a variety of above ground crops will work well in clay soil.
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Working the Soil
A soil's tilth is its ability to support seed development by allowing roots to spread and stems to emerge. Hard, compacted soils lack tilth, but providing these soil types with compost, manure, peat and other degraded and semi-degraded materials decreases soil density, allowing air to circulate and loosen soil. Horticulturists recommend disturbing clay soils as little as possible.
Compost and other amendments are applied topically and are incorporated into soil structure gradually over time. Planting a cover crop such as rye or oat grass during the fallow season provides soil with organic matter. As the crop decomposes, the roots and leaves provide the soil with beneficial aeration and nutrients.
Clay soils are wet and slow to warm in spring. Cold crops like cabbage and Brussels sprouts can be started in beds and do well under these conditions. Later in the growing season tomatoes and peppers are purchased as starts and transplanted to carefully dug and amended holes. This practice limits tilling and soil disturbance.